He's not going to die. Two Captain Commanders won't be killed off in the same arc, there's literally no one capable of doing the job besides Shunsui.
This is typical Tite Kubo. Good guy thinks he's killed Bad guy, Bad guy thinks he's killed Good guy, and it goes back and forth with different twists and the Good guy always emerges victorious. Also I don't think Shunsui Bankai is over, he said this will be the last stage, as in what's needed to kill Barro, not the actual last stage of the Bankai because the same people who accurately leaked the spoilers for 648 and 649 said his Bankai has 5 levels so there might be one more.